Adult mesenchymal stem cells (MSCs) offer enormous potential for regenerative therapies, but occur in low frequency in bone marrow, lack the ability to continuously divide under traditional ex vivo tissue expansion methods and eventually lose their differentiation potential. These factors limit the clinical efficacy of MSC therapies. The most promising approach to extend the expansion potential of MSCs in vitro is the cultivation of cells on extracellular matrix (ECM) proteins, where integrin-ligand binding between cells and the ECM are known to activate cellular processes such as proliferation, differentiation, and survival. Our objectives are to translate what is known about the role of ECM/MSC interactions in the aging process into a new generation of scaffold designs containing the appropriate chemical signals and physical features capable of regulating stem cell behavior. For this work, silk fibroin proteins will be used as a biomaterial scaffold onto which a variety of signaling molecules will be incorporated. Specific targets include cell adhesion peptides derived from collagen, and factors that activate telomerase to extend telomeres during cell division thus prolonging the life span of the cell. The chemical signaling identity and density of the peptide displays on the 3D silk scaffolds will be optimized independently in order to decouple and isolate the effects on aging of MSCs. In depth chemical and physical characterization of these modified scaffolds, and the morphology, growth rate, differentiation potential, and production of ECM proteins by the MSCs expanded on these modified 3D scaffolds will be studied and quantified along with appropriate controls. Osteogenic markers of MSCs expanded on these scaffolds will be monitored and compared to ascribe changes in cell behavior to the matrix composition. The goal of developing cell culture scaffolds that can delay senescence of MSCs to prolong their proliferative lifetimes would allow for long-term expansion of the cells ex vivo, enabling clinical use of MSCs in a broad range of cell therapies and tissue-engineered devices. Relevance to public health: Adult mesenchymal stem cells (MSCs) offer enormous potential for bone, cartilage, muscle and ligament regenerative therapies, and are easily obtained from adult bone marrow which avoids the embryonic stem cell controversy. Therefore, this project aims to address some of the clinical limitations of MSCs that currently prevent their use in cell therapies and tissue-engineered devices. Specifically, our goals are to delay the aging process in MSCs cultured ex vivo.